As filed with the Securities and Exchange Commission on August 6, 1996
                                                    Registration No. 333-8785
                                                                     --------
    

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                             ----------------------

   
                                 AMENDMENT NO. 1
                                       to
                                    FORM S-8
                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933
    

                               Tencor Instruments
             ------------------------------------------------------
             (Exact Name of Registrant as Specified in Its Charter)

               California                              94-2464767
     -------------------------------               -------------------
     (State or Other Jurisdiction of                (I.R.S. Employer
     Incorporation or Organization)                Identification No.)

              3333 Octavius Street, Santa Clara, California  95054
              ----------------------------------------------------
                    (Address of Principal Executive Offices)

                           1993 Equity Incentive Plan
                        1993 Employee Stock Purchase Plan
                      1993 Non-Employee Director Stock Plan
                      -------------------------------------
                            (Full Title of the Plan)

                                 Bruce R. Wright
                               Tencor Instruments
                              3333 Octavius Street
                         Santa Clara, California  95054
                     (Name and Address of Agent For Service)

                                 (408) 970-9500
          -------------------------------------------------------------
          (Telephone Number, Including Area Code, of Agent For Service)

                        Copy to:  Richard A. Peers, Esq.
                         Heller Ehrman White & McAuliffe
                              525 University Avenue
                        Palo Alto, California  94301-1908
                                 (415) 324-7000

   
    



                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT


ITEM 3.   INCORPORATION OF DOCUMENTS BY REFERENCE

          The following documents filed or to be filed with the Securities and
Exchange Commission (the "Commission") by the registrant are incorporated by
reference in this Registration Statement:

          (a)  The Registrant's latest annual report (Form 10-K) filed pursuant
to Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended
(the "Exchange Act"), or the latest prospectus filed pursuant to Rule 424(b)
under the Securities Act of 1933, as amended (the "Securities Act"), that
contains audited financial statements for the Registrant's latest fiscal year
for which such statements have been filed;

          (b)  All other reports filed by the Registrant pursuant to Section
13(a) or 15(d) of the Exchange Act since the end of the fiscal year covered by
the annual report or prospectus referred to in (a) above;

          (c)  The description of the Common Stock of the Registrant contained
in the Registration Statement filed under the Exchange Act registering such
Common Stock under Section 12 of the Exchange Act.

          All documents subsequently filed by the Registrant pursuant to
Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of
a post-effective amendment which indicates that all securities offered hereby
have been sold or which deregisters all securities then remaining unsold, shall
be deemed to be incorporated by reference in this Registration Statement and to
be part thereof from the date of filing of such documents.

ITEM 4.   DESCRIPTION OF SECURITIES

          Not applicable.

ITEM 5.   INTERESTS OF NAMED EXPERTS AND COUNSEL

          The validity of the Common Stock offered hereby will be passed upon
for the Registrant by Heller, Ehrman, White & McAuliffe, Palo Alto, California.
As of the date of this Registration Statement, members of Heller, Ehrman, White
& McAuliffe beneficially own 3,099 shares of the Registrant's Common Stock.

ITEM 6.   INDEMNIFICATION OF DIRECTORS AND OFFICERS

          The Articles of Incorporation of the Registrant provide that the
liability of the directors of the Registrant for monetary damages is to be
eliminated to the fullest extent possible under California law.  The Articles
also authorize the Registrant to indemnify its agents (which includes officers
and directors), whether by bylaw, agreement or otherwise, in excess of the
indemnification expressly permitted by Section 317 of the California
Corporations Code, and to advance defense expenses to its agents in connection
with such matters as they are incurred.


                                      II-2



     Section 29 of the Registrant's Bylaws provides for the indemnification of
directors and officers of the Registrant to the fullest extent permissible under
California law, and in excess of that which is expressly permitted by Section
317 of the California Corporations Code.  The Bylaws provide that the Registrant
shall indemnify its directors and officers against all expenses, judgments,
fines, settlements and other amounts actually and reasonably incurred by them in
connection with any proceeding, including an action by or in the right of the
Registrant, by reason of the fact that such person is or was a director or
officer of the Registrant or is or was serving at the request of the Registrant
as a director, officer, trustee, employee or agent of another entity.  The
Bylaws also provide that, to the fullest extent permissible under California
law, expenses incurred by a director or officer seeking indemnification under
the Registrant's Bylaws in defending any proceeding are to be advanced by the
Registrant as they are incurred, upon receipt by the Registrant of an
undertaking by or on behalf of the director or officer to repay such amount if
it is ultimately determined that the director or officer is not entitled to be
indemnified by the Registrant for those expenses.

     Section 317 of the California Corporations Code permits a corporation to
include in its charter documents and in agreements between the corporation and
its directors and officers, provisions expanding the scope of indemnification
beyond that specifically provided by the current law.

ITEM 7.   EXEMPTION FROM REGISTRATION CLAIMED

          Not applicable.

ITEM 8.   EXHIBITS

   
  5       Opinion of Heller Ehrman White & McAuliffe *

 23.1     Consent of Price Waterhouse LLP, Independent Accountants *

 23.2     Consent of Coopers & Lybrand L.L.P., Independent Accountants *

 23.3     Consent of Heller Ehrman White & McAuliffe *
          (filed as part of Exhibit 5)

 24.1     Power of Attorney (see page II-4) *

 99.1     1993 Equity Incentive Plan, as amended 

 99.1     1993 Employee Stock Purchase Plan, as amended *

 99.3     1993 Non-Employee Director Stock Plan, as amended *
- --------------

*  Previously filed
    

ITEM 9.   UNDERTAKINGS

     A.   The undersigned Registrant hereby undertakes:

          (1)  To file, during any period in which offers or sales are being
made, a post-effective amendment to this Registration Statement;

               (i)   To include any prospectus required by Section 10(a)(3) of
     the Securities Act of 1933, as amended (the "Securities Act");


                                      II-3


               (ii)  To reflect in the prospectus any facts or events arising
     after the effective date of the Registration Statement (or the most recent
     post-effective amendment thereof) which, individually or in the aggregate,
     represent a fundamental change in the information set forth in the
     Registration Statement;

               (iii) To include any material information with respect to the
     plan of distribution not previously disclosed in the Registration Statement
     or any material change to such information in the Registration Statement;

PROVIDED, HOWEVER, that paragraphs A(1)(i) and A(1)(ii) do not apply if the
information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed by the Registrant pursuant to
Section 13 or 15(d) of the Exchange Act that are incorporated by reference in
the Registration Statement.

          (2)  That, for the purpose of determining any liability under the
Securities Act, each such post-effective amendment shall be deemed to be a new
Registration Statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial BONA
FIDE offering thereof.

          (3)  To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

     B.   The undersigned Registrant hereby undertakes that, for purposes of
determining liability under the Securities Act, each filing of the Registrant's
annual report pursuant to Section 13(a) or 15(d) of the Exchange Act that is
incorporated by reference in the Registration Statement shall be deemed a new
Registration Statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial BONA
FIDE offering thereof.

     C.   Insofar as indemnification for liabilities arising under the
Securities Act may be permitted to directors, officers and controlling persons
of the Registrant pursuant to the foregoing provisions, or otherwise, the
Registrant has been advised that in the opinion of the Securities and Exchange
Commission such indemnification is against public policy as expressed in the
Securities Act and is, therefore, unenforceable.  In the event that a claim for
indemnification against such liabilities (other than the payment by the
Registrant of expenses incurred or paid by a director, officer or controlling
person of the Registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Securities
Act and will be governed by the final adjudication of such issue.


                                      II-4


                                   SIGNATURES

   
     Pursuant to the requirements of the Securities Act, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Mountain View, State of California, on this 5th day
of August, 1996.
    

                                   TENCOR INSTRUMENTS



                                      By:  /s/ Bruce R. Wright
                                        ----------------------------------
                                      Bruce R. Wright
                                      Senior Vice President, Finance and
                                      Administration, and Chief Financial
                                      Officer

   
    

     Pursuant to the requirements of the Securities Act, this Registration
Statement on Form S-8 has been signed by the following persons in the capacities
and on the dates indicated.

   
          *
- --------------------------        President, Chief             August 5, 1996
Jon D. Tompkins                   Executive Officer and
                                  Director (Principal
                                  Executive Officer)
    

   
/s/ Bruce R. Wright
- --------------------------        Senior Vice                  August 5, 1996
Bruce R. Wright                   President, Finance
                                  and Administration,
                                  and Chief Financial
                                  Officer (Principal
                                  Financial Officer)
    


                                      II-5


   
          *
- --------------------------        Vice President,              August 5,  1996
Frederick A. Ball                 Corporate Controller
                                  and Secretary
                                  (Principal Accounting
                                  Officer)
    

   
          *
- --------------------------        Vice Chairman of the         August 5, 1996
Richard J. Elkus, Jr.             Board and Executive
                                  Vice President
    

   
- --------------------------        Director                     
James W. Bagley
    

   
          *
- --------------------------        Director                     August 5, 1996
Dean O. Morton
    

   
          *
- --------------------------        Director                     August 5, 1996
Calvin F. Quate
    

   
- --------------------------        Director                 
Lida Urbanek
    

   
- --------------------------        Director                  
Renn Zaphiropoulos
    

   
By: /s/ Bruce R. Wright
   -----------------------                                     August 5, 1996
   Bruce R. Wright
   (Attorney-in-fact)
    


                                      II-6


                                INDEX TO EXHIBITS


                                                                    Sequentially
Item No.            Description of Item                            Numbered Page
- --------            -------------------                            -------------

   
  5       Opinion of Heller Ehrman White & McAuliffe * . . . . . . . . .

 23.1     Consent of Price Waterhouse LLP, Independent Accountants * . .

 23.2     Consent of Coopers & Lybrand L.L.P., Independent Accountants *

 23.3     Consent of Heller Ehrman White & McAuliffe *
           (filed as part of Exhibit 5)  . . . . . . . . . . . . . . . .

 24.1     Power of Attorney (see page II-4) *  . . . . . . . . . . . . .

 99.1     1993 Equity Incentive Plan, as amended . . . . . . . . . . . .

 99.2     1993 Employee Stock Purchase Plan, as amended *  . . . . . . .

 99.3     1993 Non-Employee Director Stock Plan, as amended *  . . . . .
- --------------

* Previously filed